1. Field of the Invention
The present invention relates to a brushless motor control apparatus, a brushless motor and a control method of the brushless motor.
2. Description of Related Art
Some blower motors are formed as a multi-phase brushless motor. In this brushless motor, a rotational position of a rotor is sensed with Hall sensors (a position sensing means), and coils of multiple phases are energized based on measurement signals of the Hall sensors, which indicate the sensed rotational position of the rotor.
In the brushless motor of the above type, a mechanical positional deviation of any one of the Hall sensors from its proper position may cause a deviation in the energization timing for energizing the corresponding one of the coils of the multiple phases from its appropriate timing, thereby resulting in generation of a noisy sound or a vibration of the motor.
In view of the above disadvantage, for instance, Japanese Unexamined Patent Publication No. 2003-47277A provides a technique of correcting the positional deviation of the Hall sensor for implementing the appropriate energization timing.
However, in this technique, a relative positional deviation between the Hall sensor and the rotor magnet is not corrected. In a case where a positional accuracy of the Hall sensor is finely set to avoid the relative positional deviation between the Hall sensor and the rotor magnet, the costs in the manufacturing process are substantially disadvantageously increased. Furthermore, in order to correct the relative positional deviation between the Hall sensor and the rotor magnet, the amount of deviation in the position of the Hall sensor from its appropriate position is stored as a correction data, value in an external storage device (e.g., EEPROM) in an inspection process after installation of the Hall sensor to the motor. Then, the energization of the coils is performed based on the correction data value. In such a case, the external storage device (e.g., the EEPROM) is disadvantageously expensive, and the external storage device (e.g., the EEPROM) has a disadvantageously low heat resistance. Therefore, the above technique is not suitable for the brushless motor, the temperature of which becomes disadvantageously high.
In view of the above disadvantages, for instance, Japanese Unexamined Patent Publication No. H09-47066A provides a technique of correcting the relative positional deviation between the Hall sensor and the rotor magnet based on a value of correction data (hereinafter, referred to as a correction data value) that is created with reference to an output signal of the Hall sensor and a zero-cross point of an induced voltage, which is generated in a state where the energization of the coils of all the phases are turned off.
In a case where the correction is made based on the correction data value, which is obtained in one time, when a noise is generated at the time of obtaining the correction data value, the correction is made based on the correction data value, which includes the noise. Thereby, in such a case, the appropriate correction may not be possible. There is proposed a technique of correcting the deviation based on an average value of the correction data values, which are generated by obtaining the correction data value multiple times to improve the reliability of the correction data value and thereby to accurately correct the positional deviation. In such a case, the correction data value is obtained multiple times, so that the time period of turning off of the energization of the coils is lengthened.
Furthermore, in the case of Japanese Unexamined Patent Publication No. H09-47066A where the energization of, the coils of all the phases is turned off in the brushless motor at the time of obtaining the correction data value, the brushless motor may possibly be stalled (i.e., decelerated and stopped) at the time of sensing the zero-cross point of the induced voltage. When the time period of turning off of the coils of all the phases is lengthened, the deceleration of the rotational speed of the motor is increased, and the rotation is unsmoothed. Thereby, a noisy sound may possibly be generated.